JP2512919B2 - Refining method for stainless steel with less oxidation of valuable metals such as Cr during decarburization of molten steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention is for refining stainless steel in which valuable metals such as Cr are less oxidized during decarburization of molten steel used for refining stainless steel. It is about the method.

(Prior Art) Conventionally, as a refining method for various steels, there are a converter steelmaking method and an electric furnace steelmaking method, which are mainly used in the production of mass-produced steels. In addition to the above converter steelmaking method and electric furnace steelmaking method,
D refining method (vacuum decarburization method), IOD refining method (argon / oxygen decarburization method), etc.

Among these, for example, in the AOD refining method, an inert gas (Ar, N ₂ ) is blown into a steel bath together with oxygen gas, CO partial pressure is reduced, and decarburization is performed while suppressing oxidation loss of Cr,
In order to efficiently carry out decarburization at this time, it is a refining method in which the O ₂ / Ar ratio blown into the steel bath is lowered as decarburization proceeds from the high carbon region to the low carbon region. In addition, there is also a CLU refining method that uses steam as a dilution gas instead of expensive Ar.

This AOD refining method does not have a function to heat molten steel from the outside, and in order to compensate for the heat during refining, generally carburizing is performed as necessary before starting refining. Therefore, the average C content in molten steel is 1.0 to
The content was 2.0% by weight and the heat of oxidation reaction of C was used in refining.

Therefore, it takes a long time to decarburize, it is necessary to partially oxidize Cr for heat compensation, and then re-reduce with expensive Si in a later process. There was a problem that it was difficult to control the temperature at that time.

In addition to the above-mentioned AOD refining method, not only in the refining method of various steels but also in order to compensate for the heat necessary for refining, electric heating is adopted, or oxygen is generated to generate reaction heat of C and other metals. It is also used to inject, but it is used for reducing and recovering valuable metals, such as poor energy intensity, large oxidation loss of valuable metals, etc.
There was a problem that the required amount of Si was large.

(Object of the Invention) The present invention has been made by focusing on the above-mentioned conventional problems, and it is possible to shorten the decarburization time during the refining of stainless steel, and the amount of oxidation loss of valuable metals such as Cr. And the amount of reducing agent used can be reduced at the same time as the time required for the reduction of the oxide is reduced, and the refining of stainless steel in which valuable metals such as Cr are less oxidized during the decarburization period of molten steel It is intended to provide a method.

[Structure of the Invention] (Means for Solving Problems) The refining method for stainless steel in which valuable metals such as Cr are less oxidized during decarburization of molten steel according to the present invention is a tuyere opened in molten steel in a furnace. When carrying out decarburization refining of stainless steel while forcibly stirring the molten steel with the oxidizing gas or the oxidizing gas and the inert gas blown into the molten steel through a fuel source such as heavy oil, pulverized coal or natural gas, Due to the flame from the combustion burner that injects the fire caused by the combustion of the oxidizing gas of the fuel source into the furnace containing the molten steel with a high carbon content, the steel bath surface with the heat receiving area expanded by the forced stirring On the other hand, while supplying heat, the carbon in the molten steel with a high carbon content is oxidized to perform decarburization refining from the molten steel with a high carbon content into the molten steel with a low carbon content, and the oxidized Cr is oxidized. Etc. In which is characterized in that so as to appropriately implement the reduction refining valence metal.

The furnace to which the refining method of stainless steel in which the oxidation of valuable metals such as Cr in the decarburizing period of the molten steel according to the present invention is applied is, in addition to those having an external heating function such as an electric furnace, as described above, It can also be applied to AOD furnaces, CLU furnaces, VOD furnaces and converters that do not have a heating function from the outside.

Then, gas is blown into the molten steel through tuyere opening in the molten steel in the furnace to forcibly stir the molten steel, thereby expanding the heat receiving area of the molten steel upper surface, but as the gas in this case, , An oxidizing gas having an action of causing a decarburization reaction in molten steel (such as an O ₂ or O ₂ -enriched gas) can be used, or an inert gas (Ar, N ₂ having an action of forced stirring for molten steel) Alternatively, these enriched gases, etc.) can be used, and further, an oxidizing gas and an inert gas supplied so as to surround the oxidizing gas are used at the same time in order to protect tuyere for blowing the oxidizing gas. You can also

And, in the present invention, when carrying out decarburization refining of stainless steel while forcibly stirring the molten steel by the gas blown into the molten steel in the furnace, heavy oil, pulverized coal, a combustible fuel source such as natural gas And a steel bath surface having an expanded heat-receiving area by the forced agitation by a flame from a combustion burner that injects a flame generated by combustion of the fuel source with an oxidizing gas into a furnace containing molten steel with a high carbon content. While supplying heat to the steel, the carbon in the molten steel with a high carbon content is oxidized to perform decarburization refining from the molten steel with a high carbon content to a molten steel with a low carbon content. , In this case, as the oxidizing gas supplied to the combustion burner, it is not impossible to use air, but more desirably, 100% by volume O ₂ gas, or 3
A mixture of nonflammable gases (eg N ₂ , Ar, etc.) containing 0% by volume or more of O ₂ is used, whereby a high temperature flame is obtained.

Further, in the C content region in the molten steel in which the decarburization reaction during decarburization refining is the O ₂ supply-controlling rate, usually in the region where the C content is about 0.20 wt% or more, the theoretical oxygen demand for the fuel source is higher than the theoretical oxygen demand. By supplying a large amount of O ₂ source, the CO generated on the steel bath surface by the decarburization reaction is further burned, and the reaction heat energy generated when it is converted into CO ₂ is effectively utilized, and the combustion energy is forced to the above. It is preferable that the molten steel temperature is raised by supplying the molten steel to the surface of the steel bath whose heat-receiving area is expanded by stirring to further accelerate the decarburization reaction while suppressing the oxidation of Cr.

In this case, when supplying more O ₂ source than the theoretical oxygen demand for the fuel source, it is possible to increase the O ₂ source supply amount by the oxidizing gas supplied to the combustion burner, It is also possible to supply an O ₂ source onto the steel bath surface separately from the burner, and it is within the scope of the present invention.

Further, in the method for refining stainless steel according to the present invention, it is particularly desirable that the fire from the combustion burner is set to be jetted toward the steel bath surface by a counter method.

In addition, although it is generally possible to adopt arc heating as a heating source, in the present invention, since it is a requirement to forcibly stir the molten steel in order to expand the heat receiving area of the molten steel, such forced stirring is also required. Since it is difficult to use arc heating with and, even if arc heating is used to melt raw materials such as scrap, it was decided to use heating with a combustion burner during subsequent refining such as decarburization.

The refining apparatus for carrying out the refining method of stainless steel in which valuable metals such as Cr are less oxidized in the decarburization period of the molten steel according to the present invention is a decarburization refining from molten steel having a high carbon content to molten steel having a low carbon content. During the reduction refining of valuable metals such as oxidized Cr and the like, and a furnace body containing molten steel,
A gas supply that has tuyere opening in the molten steel in the furnace and blows an oxidizing gas or an oxidizing gas and an inert gas into the molten steel through the tuyere to forcibly stir the molten steel and decarburize the gas. Means, a combustion burner for supplying heat to the steel bath surface whose heat receiving area is enlarged by the forced stirring, a fuel supply means for supplying a fuel source to the combustion burner, and an O ₂ source for the combustion burner Fuel source for supplying O ₂ source for combustion, CO amount measuring means for measuring CO amount in exhaust gas, CO generated from steel bath surface during decarburization refining
It is possible to provide an O ₂ source supply means for CO combustion at the time of decarburization, which is converted into ₂ , for supplying an O ₂ source to the steel bath surface separately from the combustion burner as needed. The case where an O ₂ source supply means is provided is also included.

FIG. 1 is a view showing an embodiment of the present invention. The stainless steel refining apparatus shown in FIG. 1 which is directly used for carrying out the method for refining stainless steel according to the present invention is a molten steel 1
Has a furnace lid 3 at the upper end of the furnace body 2 for accommodating the gas, and an inner tube 4a for blowing O ₂ gas, which is an oxidizing gas, and an outer tube for blowing Ar gas, which is an inert gas, on the lower side of the furnace body 2. The tuyere 4 composed of 4b and 4b forms a gas feeding means for blowing gas into the molten steel 1 in the furnace to forcibly stir the molten steel 1 and cause decarburization. There is.

Further, an inclined tap hole 5 is provided on the upper portion of the furnace body 2.

Further, the furnace lid 3 is provided with a combustion burner 6 for supplying heat to the steel bath surface of the molten steel 1 whose heat receiving area is enlarged by the forced stirring. This combustion burner 6 has a connection port 6a to the fuel source supply means, a connection port 6b to the O ₂ source supply means, and also has a cooling water inlet port 6c and an exhaust port 6d for cooling. It has a possible structure.
In this case, the combustion burner 6 is installed in the vertical direction, and the flame 7 from the combustion burner 6 is set to be jetted toward the surface of the molten steel 1 by the counter blow method. That is, in order to efficiently transfer and supply heat to the steel bath surface whose heat-receiving area has been expanded by forced agitation, and to make the O ₂ flow in the opposite direction to the CO gas flow direction generated on the net bath surface. The flame 7 is set to be jetted by a counter blow method so that the source can be blown.

The fuel source supply means for sending the fuel source to the combustion burner 6 includes a fuel source supply pipe 11, a flow meter 12,
A valve 13, a fuel tank 14, a pressurized medium supply pipe 15 such as N ₂ gas, a valve 16, a pressure gauge 17, and the like. Further, the O ₂ source supply means for sending an O ₂ source (100 volume% O ₂ gas or a mixed gas containing O ₂ gas) to the combustion burner 6 is an O ₂ source supply pipe 21, valves 22, 23. , Flow meter 24, etc.

Further, the furnace lid 3 installed at the upper end of the furnace body 2 is provided with an exhaust gas outlet 3d in addition to the insertion hole 3a for inserting the fuel burner 6 therein, and the exhaust gas is introduced into the dust collecting hood 25. I am guided. Then, the exhaust gas outlet 3b is provided with a CO / CO ₂ meter 26 as a CO amount measuring means for measuring the CO / CO ₂ ratio in the exhaust gas.

Therefore, when refining stainless steel, O ₂ gas, which is an oxidizing gas, is blown into the molten steel 1 housed inside the furnace body 2 from the inner pipe 4a of the tuyere 4 and at the same time, an inert gas is fed from the outer pipe 4b. Blowing Ar gas that is
The fuel 7 such as heavy oil, pulverized coal, and natural gas, and the flame 7 injected from the combustion burner 6 supplied with the O ₂ source are forcibly stirred to the steel bath surface whose heat receiving area is expanded by this forced stirring. In order to compensate for the heat required during refining by increasing the molten steel temperature and replacing the conventional heat compensation with the heat of oxidation reaction of C, it is possible to reduce the initial C content to, for example, about 0.8% by weight. This makes it possible to shorten the decarburization time, suppress the oxidation of valuable metals such as CR, reduce the amount of Si required for the reduction of the valuable metals, and reduce the amount of slag produced to reduce the slag removal time. Achieve shortening and improvement of energy intensity In addition, by reducing the above time and suppressing oxides such as Cr, the melting loss of refractory materials can be reduced. Furthermore, effective utilization of Cr ore will be possible.

Then, during the refining, O _{2 is applied to the} combustion burner 6.
As the oxidizing gas supplied through the source supply pipe 21, a mixed gas of 30% by volume or more of O ₂ and other noncombustible gas (N ₂ , Ar, etc.) or 100% by volume of O ₂ gas is used. It is also desirable to be able to obtain the flame 7 to promote the decarburization reaction and prevent the oxidation of valuable metals such as Cr.

Further, during the refining, in the C content region (usually C ≧ 0.20% by weight) in the molten steel where the decarburization reaction is an O ₂ supply rate speed, the supply of the O ₂ source from the inner pipe 4a of the tuyere 4 is performed. Since the CO gas that is found in the CO2 is generated on the steel bath surface, the amount of CO generated is calculated as CO / CO ₂
Measured by a meter 26, from the O ₂ source supply pipe 21 connected to the combustion burner 6 or from an O ₂ source injection nozzle (not shown) installed separately from the combustion burner 6, the amount of oxygen required for the fuel source is higher than the theoretical oxygen demand. The O ₂ source is supplied onto the bath surface of the molten steel 1 to burn the CO generated from the steel bath surface to produce CO
It was converted to _2, by utilizing the heat of reaction during this increases the temperature of the molten steel 1 efficiently, thereby also promoting decarburization and
It is also desirable to suppress the oxidation of valuable metals such as Cr, and thereafter, it is desirable to appropriately carry out reduction refining of the valuable metals such as oxidized Cr.

(Example) In this example, 23 ton of molten steel was put into the furnace body 2 and
Smelting of 304 equivalent material was carried out in four stages. At this time, the C content in the molten steel before the start of refining was 0.8% by weight, and O ₂ gas was blown from the inner pipe 4a of the tuyere 4 at the same time as the outer pipe.
Blow Ar gas from 4b to bring molten steel 1 into a forced stirring state,
Refining was performed while heating the molten steel 1 by injecting a flame 7 from a combustion burner (capacity; heavy oil 22 l / min) 6.

For comparison, the content of C in the molten steel before the start of refining is 1.5% by weight, which is based on the conventional AOD refining method.
Used as it is, and the molten steel (1) and forced stirring state by blowing an inner tube outer tube at the same time blown with O ₂ gas from (4a) (4b) than Ar gas tuyere (4), a combustion burner (6 ) Was used for refining.

The refining pattern at this time is shown in Table 1 and FIG. Table 2 shows the thermal efficiency in the first and second stages of refining. In Table 2, the total effective heat quantity is the total heat quantity required for molten steel temperature rise + alloy melting + smelting agent melting.
Further, the amount of Cr oxidation in the example of the present invention could be suppressed to half of that in the comparative example by shortening the time. further,
The heat deposition efficiency in the combustion burner 6 was estimated to be 40%.

As shown in Table 1, in the examples of the present invention, since the heat compensation during refining is performed by the flame 7 from the combustion burner 6, the C content in the molten steel before refining is changed from the conventional 1.5% by weight. Since it is possible to reduce it to 0.8% by weight, the C content in the molten steel after the completion of the first and second stages is
It was possible to reduce the decarburization time to about 0.3% by weight by about 7 minutes.

Further, as shown in FIG. 2, in the examples of the present invention, since the amount of Cr loss in the molten steel is small, that is, the amount of oxidation of Cr is small, the time required for subsequent Cr reduction is about 1% as shown in Table 1. I was able to save 3 minutes.

Therefore, by shortening the decarburizing time and suppressing Cr oxidation in the first and second stages of refining, it is possible to reduce the refractory melting loss and the Si source unit, and the heat compensation by the combustion burner 6 It also led to effective utilization of Cr ore.

Further, as described above, in the embodiment of the present invention, as shown in FIG. 2, since the amount of Cr oxidation is small, it is necessary for the subsequent Cr reduction.
Compared to the comparative example, the amount of Si source used is about 3.5 Kg / ton of molten steel
It was possible to shorten the slag removal time by about 2 minutes as shown in Table 1. Also the sum
By shortening the time of 12 minutes, it was possible to reduce the Si unit consumption and significantly extend the life of the refractory.

[Effects of the Invention] As described above, according to the method for refining stainless steel in which valuable metals such as Cr are less oxidized during the decarburization period of the molten steel according to the present invention, the molten steel is passed through the tuyere opening in the molten steel in the furnace. When carrying out decarburization refining of stainless steel while forcibly stirring the molten steel with the oxidizing gas blown into it or the oxidizing gas and inert gas, use a fuel source such as heavy oil, pulverized coal, natural gas and carbon. Due to the flame from the combustion burner that injects the flame generated by the combustion of the oxidizing gas of the fuel source in the furnace containing the molten steel with a large content, heat is applied to the steel bath surface whose heat receiving area is expanded by the forced stirring. Is carried out to oxidize the carbon in the molten steel with a high carbon content while performing decarburization refining from the molten steel with a high carbon content to a molten steel with a low carbon content, and the oxidized Cr
Reducing refining of valuable metals such as the above is carried out appropriately, so that when decarburizing and refining steel, the C content in molten steel before decarburizing and refining is 1.0 so that the thermal compensation by the C can be sufficiently obtained. Since it is not necessary to control to about 2.0% by weight and the heat compensation is performed by the combustion burner, the C content in the molten steel before decarburizing and refining can be made smaller than before, It is possible to shorten the decarburization time.By reducing this time, the amount of valuable metals such as Cr oxidized is reduced, the oxidation loss of valuable metals such as Cr is reduced, and the valuable metals such as Cr are reduced. It is possible to reduce the amount of reducing agent added and the reduction time during reduction refining for the re-reduction of slag.By reducing the amount of reducing agent used, the amount of flags generated also decreases and the slag is removed. Excellent effects such as it is possible to realize the shortening between is provided.

[Brief description of drawings]

FIG. 1 is an explanatory view of a vertical cross section of a stainless steel refining apparatus used in one embodiment of the present invention, and FIG. 2 is an amount of [Cr] in molten steel and [C] in a refining process in Examples and Comparative Examples of the present invention. ] It is a graph which shows the change of the amount and molten steel temperature. 1 ... Molten steel, 2 ... Furnace body, 3 ... Furnace lid, 4 ... Tuyere (gas feeding means), 5 ... Steel tap, 6 ... Combustion burner, 7 ... Flame, 11 ... Fuel source supply pipe (fuel source supply means), 21 …… O ₂ source supply pipe (O ₂ source supply means), 26 …… CO / CO ₂ meter (CO amount measuring means).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Ishii 18 Minamikamochi, Kagiya-cho, Tokai-shi, Aichi (56) References JP-A-47-7301 (JP, A)

Claims (6)

(57) [Claims] 1. Decarburizing and refining of stainless steel while forcibly stirring the molten steel by the oxidizing gas or the oxidizing gas and the inert gas blown into the molten steel through tuyeres opening in the molten steel in the furnace. When using a fuel source such as heavy oil, pulverized coal, natural gas, etc., and a flame from a combustion burner that injects a fire caused by combustion of the oxidizing gas of the fuel source into a furnace containing molten steel with a high carbon content , The carbon in the molten steel having a high carbon content is oxidized while supplying heat to the steel bath surface whose heat receiving area has been expanded by the forced agitation to reduce the carbon content from the molten steel having a high carbon content. Smelting of stainless steel with little oxidation of valuable metals such as Cr during decarburization of molten steel, characterized by performing decarburization refining of molten steel and appropriately performing reduction refining of valuable metals such as oxidized Cr Method. 2. A high-temperature flame is obtained by using an oxygen-enriched mixed gas containing 30% by volume or more of O ₂ as an oxidizing gas supplied to a combustion burner.
Item 6. A method for refining stainless steel in which valuable metals such as Cr are less oxidized during the decarburization period of the molten steel according to the item. 3. A flame from a combustion burner is set so as to be directed toward a steel bath surface. In the decarburizing period of molten steel according to claim (1) or (2), Cr, etc. A method for refining stainless steel with less oxidation of valuable metals. 4. In a C content region in molten steel in which decarburization reaction is an O ₂ supply-controlling rate, more O ₂ source than the theoretical oxygen demand for a fuel source is supplied. A method for refining stainless steel in which valuable metals such as Cr are less oxidized during the decarburization period of the molten steel according to any one of (1) to (3). 5. The supply of the O ₂ source is carried out from the combustion burner on the surface of the steel bath, and oxidation of valuable metals such as Cr during decarburization of the molten steel according to claim (4). How to refine less stainless steel. 6. An O ₂ source is supplied on a steel bath surface separately from a combustion burner, and valuable metals such as Cr are added during decarburization of molten steel according to claim (4). A method of refining stainless steel with little oxidation.